Roller bearing

ABSTRACT

In a roller bearing, surface layers are formed on the inner surfaces of flanges which confront with the end faces of cylindrical rollers. The surface layers contain solid lubricant. The end faces of the cylindrical rollers are brought into slide contact with the surface layers. Hence, even when the roller bearing is insufficiently lubricated, the temperature rise is effectively suppressed, thus being free from the occurrence of seizure.

This application is a continuation of application Ser. No. 08/675,278filed Jul. 1, 1996, now U.S. Pat. No. 5,669,719, which is a continuationof application Ser. No. 08/271,972 filed on Jul. 8, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to roller bearings (including acylindrical roller bearing and a conical roller bearing) used in partsof a variety of machines which support rotary shafts under great thrustload is applied.

For instance, in the case where, as shown in FIG. 3, a rotary shaft 1forming a part of a machine tool is rotatably supported in a housing 2,a taper roller bearing 3 as shown in FIG. 4 or 5 is generally used. Thetaper roller bearing 3 provides: an inner race 5 having an inner raceway5 in the outer cylindrical surface; an outer race 7 having an outerraceway 6 in the inner cylindrical surface; and a plurality of taperrollers 8, 8, 8 . . . which are rollingly provided in the space definedby the inner raceway 4 and the outer raceway 6. More specifically, thetaper rollers 8 are rollingly held in pockets 10, 10, 10, . . . formedin a cage 9. Flanges 11a and 11b are radially outwardly extended fromboth edges of the outer cylindrical surface of the inner race 5 in sucha manner that the inner surfaces of the flanges 11a and 11b areconfronted with the end faces of the taper rollers 8, so as to preventthe latter 8 from shifting axially (or to the right or to the left inFIG. 3 or 4).

As shown in FIG. 3, the taper roller bearing 3 is fitted between therotary shaft 1 and the housing 2; more specifically, the inner race 5 isfitted on the outer cylindrical surface of the rotary shaft 1 while theouter race 7 is fitted in the inner surface of the housing 2. Thus, therotary shaft 1 has been rotatably supported in the housing 2.

When a roller bearing, such as the taper roller bearing described withreference to FIGS. 3 and 4, is turned, its temperature is often greatlyraised because of the friction between the end faces of the rollers suchas the rollers 8 and the inner surfaces of the flanges which are formedalong the raceway. In the case of the taper roller bearing as shown inFIGS. 3 and 4, the inner race 5 is pushed to the left in FIG. 3 or 4 forthe purpose of pre-loading it, as a result of which the end faces 12 ofthe taper rollers 8, which are larger in diameter than the other endfaces (hereinafter referred to as "large-diameter end faces 12", whenapplicable) and the inner surface of the flange 11a are liable to bebrought into contact with each other, thus producing friction betweenthem to raise the temperature of the taper roller bearing.

In the case of a cylindrical roller bearing providing cylindricalrollers, parallel rollers constant in diameter, during operation thecentral axes of the cylindrical rollers are often caused to be not inparallel with the central axis of the inner race and the outer race;that is, so-called "skewing" occurs. Upon occurrent of "skewing" occurs,the end faces of the cylindrical rollers and the inner surfaces of theflanges are rubbed by each other, thus causing friction between them.The friction thus caused will raise the temperature of the cylindricalroller bearing.

In order to eliminate the above-described difficulty accompanying aroller bearing, the following method has been employed in the art: Theend portions of the rollers are designed as follows: That is, thecontact areas of the end faces of the rollers with the inner surfaces ofthe flanges are reduced thereby to decrease the frictional area thereofand to allow oil films to be readily formed at the contact regionsthereof, whereby the temperature rise of the roller bearing due to thefriction is suppressed. However, as the contact areas are decreased inthe above-described manner, the contact regions are increased in surfacepressure as much. Hence, if the lubrication is insufficient, then at thecontact regions the metal parts are liable to directly contact with eachother, thus generating heat to the extent that they are seized. Theabove-described phenomenon occurs with roller bearings made of bearingsteel, and it occurs more significantly with roller bearings which areformed by using materials such as ceramic material large in the modulusof longitudinal elasticity.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a roller bearing which is free from the above-describeddifficulties accompanying a conventional roller bearing.

A roller bearing of the present invention, similarly as in theabove-described conventional one, provides: an inner race having aninner raceway on the outer cylindrical surface thereof; an outer racehaving an outer raceway on the inner cylindrical surface thereof; aplurality of rollers rotatably provided between the inner raceway andthe outer raceway; and a flange extended from at least one of both edgesof either of the outer cylindrical surface of the inner race and theinner cylindrical surface of the outer race in such a manner that theinner surface of the flange is confronted with the end faces of therollers.

The specific feature of the roller bearing according to the presentinvention resides in that a surface layer of solid lubricant is formedon either of the inner surface of the flange and the end faces of therollers which are confronted with the inner surface.

The roller bearing of the present invention, designed as described aboveis advantageous in that, even when the end faces of the rollers rub theinner surface of the flange, the frictional force applied to the rubbedsurface is small, and accordingly the amount of heat generated therebyis also small; that is, the temperature rise of the bearing iseffectively suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a fragmentary sectional view of a first embodiment of thepresent invention;

FIG. 2 is a fragmentary sectional view of a second embodiment of thepresent invention;

FIG. 3 is a sectional view for a description of the use of a taperroller bearing, one kind of roller bearing; and

FIG. 4 is a perspective view, with parts cut away, showing the taperroller bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of the present invention, a cylindricalroller bearing to which the technical concept of the invention isapplied. The cylindrical roller bearing 13 provides: an inner race 5ahaving an inner raceway 4a in the outer cylindrical surface; an outerrace 7a having an outer raceway 6a in the inner cylindrical surface; anda plurality of cylindrical rollers 14 which are rollingly providedbetween the inner raceway 4a and the outer raceway 6a. Morespecifically, the cylindrical rollers 14 are rollingly held in pockets10a, 10 a, 10a, . . . formed in a cage 9a. A flange 15 is radiallyoutwardly extended from one edge (the left edge in FIG. 1) of the outercylindrical surface of the inner race 5a. Flanges 16a and 16b areradially inwardly extended from both edges of the inner cylindricalsurface of the outer race 7a.

In the above-described cylindrical roller bearing 13 according to thepresent invention, it should be noted that a surface layer 17 of solidlubricant is formed on the inner surface of the flange 15 of the innerrace 5a which confronts with the first end faces of the cylindricalrollers 14; and another surface layer 17 of solid lubricant is formed onthe inner surface of the flange 16b of the outer race 7a which flange islocated on one side (on the right side in FIG. 1) which is opposite tothe side (the left side in FIG. 1) where the flange 15 is provided.

The solid lubricant forming those surface layers is preferablymolybdenum disulfide (MoS₂), or polytetrafluoro-ethylene (PTFE), or amixture of them. In order to form the surface layers 17 and 17, it ispreferable to mix the above-described solid lubricant in themacromolecular matrix of epoxy, polyamide or the like. In addition, itis preferable that an intermediate layer of phosphate compound orsulfide compound is formed between each of the surfaces layers 17 and 17and each of the inner surfaces of the flanges 15 and 16b, to enhance thebinding of the surface layers 17 and 17 to the flanges 15 and 16b.

The cylindrical roller bearing 13 designed as described above isadvantageous as follows: Even when the end faces of the cylindricalrollers 14 and the inner surfaces of the flanges 15 and 16b are rubbedby each other, the frictional forces acting on the contact surfaces ofthem are small, and accordingly the amount of heat generated thereby isalso small. Hence, with the same thrust load applied to the cylindricalroller bearing, the temperature rise of the cylindrical roller bearing13 of the present invention is smaller than that of the conventionalone. In addition, with the same temperature rise, the thrust load whichcan be applied to the cylindrical roller bearing of the presentinvention is larger than that which can be applied to the conventionalone.

FIG. 2 shows a second embodiment of the present invention, a taperroller bearing to which the technical concept of the invention isapplied. The taper roller bearing 3 is equal in fundamental structure tothe above-described conventional one. Therefore, only the specificfeature of the taper roller bearing 3 will be described with referenceto FIG. 2, in which parts corresponding functionally to those which havebeen described with reference to FIG. 1 (the first embodiment) aretherefore designated by the same reference numerals or characters.

Similarly as in the case of the above-described first embodiment, asurface layer 17 is formed on the inner surface of the flange 11a whichconfronts with the large-diameter end faces of the taper rollers 8.Hence, the taper roller bearing 3 is advantageous as follows: Even whenthe end faces of the taper rollers 8 and the inner surface of the flange11a are rubbed by each other, the frictional forces acting on thecontact surfaces thereof are small, and accordingly the amount of heatgenerated thereby is small; that is, the temperature rise of the taperroller bearing 3 is sufficiently suppressed. In addition, a great thrustload can be applied to the taper roller bearing 3.

EXAMPLES

As conducive to a full understanding of the present invention, severalconcrete example of the roller bearings of the invention will bedescribed. As for first and second examples, cylindrical roller bearings13 as shown in FIG. 1 were formed which were 52 mm in outside diameter,25 mm in inside diameter and 16 mm in width, and had eleven (11)cylindrical rollers 14. The surfaces layers 17 and 17 were formed byprocessing the inner surfaces of the flanges 15 and 16b of thecylindrical roller bearings 13 as follows:

In the Case of the First Example

Firstly the inner surfaces of the flanges 15 and 16 were subjected tophosphating, and then a polyamideimide DMF (dimethylformamide) solution,in which PTFE particles were dispersed, was sprayed on the innersurfaces thus processed to a thickness of 10 μm, to form DMF solutionlayers on them. Finally the resultant polyamideimide resin on the innerrace 5a and the outer race 7a was thermally set at a temperature of 180°C. As a result, the inner race 5a and the outer race 7a having thesurface layers 17 and 17 were obtained.

In the Case of the Second Example

Firstly the inner surfaces of the flanges 15 and 16 were subjected tosulphurizing, and then an epoxy and ethyl acetate solution, in whichmolybdenum disulfide particles were dispersed, was sprayed on the innersurfaces to a thickness of 10 μm. Finally, the resultant epoxy resin onthe inner race 5a and the outer race 7a was thermally set at atemperature of 150° C. As a result, the inner race 5a and the outer race7a having the surface layers 17 and 17 were obtained.

The above-described two kinds of cylindrical roller bearings having thesurface layers 17 according to the present invention, and a cylindricalroller bearing having no such surface layers which constitutes a firstcomparative example were given a rotation test (inner race rotation).The conditions of the rotation test were as listed below:

    ______________________________________                                        Radial load   20 kg                                                           Thrust load   10 kg and 50 kg                                                 Rotation speed                                                                              3000 r.p.m.                                                                   (the peripheral speed of the                                                  inner raceway at the middle                                                   being 4.8 m/s)                                                                1000 r.p.m.                                                                   (the peripheral speed of the                                                  inner raceway at the middle                                                   being 1.6 m/s)                                                  Lubrication   20 μl of paraffin mineral oil, applied                                     uniformly to the cylindrical rollers                                          and the raceways (boundary                                                    lubrication)                                                    ______________________________________                                    

The results of the rotation test are as indicated in the following Table1: In Table 1, the term "outer race saturation temperature" as usedherein is intended to mean the temperature at which the amount of heatradiation and the amount of heat generation are canceled out by eachother, so that the temperature of the outer race 7 is no longerincreased; and the term "total number of revolutions" as used herein isintended to mean the number of revolutions which are made by the innerrace 5a until the cylindrical roller bearing 3 is vibrated being seized.

                                      TABLE 1                                     __________________________________________________________________________               Example 1    Example 2    Comparative example 1                               Outer race   Outer race   Outer race                               Rotation   saturation                                                                          Total number                                                                         saturation                                                                          Total number                                                                         saturation                                                                           Total number                      speed                                                                              Thrust load                                                                         temperature                                                                         of     temperature                                                                         of     temperature                                                                          of                                (r.p.m.)                                                                           (kg)  (°C.)                                                                        revolutions                                                                          (°C.)                                                                        revolutions                                                                          (°C.)                                                                         revolutions                       __________________________________________________________________________    1000 10    33    10 × 10.sup.6 ≦                                                         34    10 × 10.sup.6 ≦                                                         45        8 × 10.sup.6                  50    40    10 × 10.sup.6 ≦                                                         41    10 × 10.sup.6 ≦                                                         69      0.1 × 10.sup.6             3000 10    43    7.5 × 10.sup.6                                                                 49    4.6 × 10.sup.6                                                                 75     0.250 × 10.sup.6                 50    60    1.8 × 10.sup.6                                                                 62    1.2 × 10.sup.6                                                                 90     0.007 × 10.sup.6            __________________________________________________________________________

As is apparent from Table 1, in the case of the first and secondexamples of the cylindrical roller bearings according to the presentinvention, the temperature rise was suppressed, so that the bearingswere scarcely seized. That is, those bearings were lengthened in servicelife as much.

Next, as for third and fourth examples, taper roller bearings 3 as shownin FIG. 2 were formed which were 52 mm in outside diameter, 25 mm ininside diameter, 16° in contact angle, 1°55' in the conical angle ofeach taper roller, and 11.8 mm in the point of action. The surface layer17 of solid lubricant was formed on the inner surface of the flange 11aby processing it as follows:

In the Case of the Third Example

Firstly the inner surface of the flange 11a was subjected tophosphating, and then a polyamideimide DMF solution, in which PTFEparticles were dispersed, was sprayed on the inner surface of the flange11a to a thickness of 10 μm. Finally the resultant polyamideimide resinon the inner race 5a was thermally set at a temperature of 180° C. As aresult, the inner race 5a having the surface layer 17 was obtained.

In the Case of the Fourth Example

Firstly the inner surface of the flange 11a was subjected tosulphurizing, and then an epoxy and ethyl acetate solution, in whichmolybdenum disulfide particles were dispersed, was sprayed on the innersurface to a thickness of 10 μm. Finally, the epoxy resin on the innerrace 5a was thermally set at a temperature of 150° C. As a result, theinner race 5a having the surface layer 17 was obtained.

The above-described third and fourth examples, the taper roller bearingshaving the surface layer 17 according to the present invention, and asecond comparative example, a taper roller bearing having no suchsurface layer were given a rotation test (inner race rotation). Theconditions of the rotation test were as listed below:

    ______________________________________                                        Radial load   None                                                            Thrust load   50 kg, 100 kg, 150 kg, 200 kg, 300 kg                           Rotation speed                                                                              1000 r.p.m.                                                                   (the peripheral speed of the                                                  inner raceway at the middle                                                   being 1.6 m/s)                                                                2000 r.p.m.                                                                   (the peripheral speed of the                                                  inner raceway at the middle                                                   being 3.2 m/s)                                                  Lubrication   20 μl of paraffin mineral oil, applied                                     uniformly to the cylindrical rollers                                          and the raceways (boundary                                                    lubrication)                                                    ______________________________________                                    

The results of the rotation test are as indicated in the following Table2: In Table 2, the terms "outer race saturation temperature" and "totalnumber of revolutions" are equal to those in Table

                                      TABLE 2                                     __________________________________________________________________________               Example 3    Example 4    Comparative example 2                               Outer race   Outer race   Outer race                               Rotation   saturation                                                                          Total number                                                                         saturation                                                                          Total number                                                                         saturation                                                                           Total number                      speed                                                                              Thrust load                                                                         temperature                                                                         of     temperature                                                                         of     temperature                                                                          of                                (r.p.m.)                                                                           (kg)  (°C.)                                                                        revolutions                                                                          (°C.)                                                                        revolutions                                                                          (°C.)                                                                         revolutions                       __________________________________________________________________________    1000 100   30    4 × 10.sup.6 ≦                                                          24    4 × 10.sup.6 ≦                                                          35        4 × 10.sup.6                                                         ≦                               200   44    4 × 10.sup.6 ≦                                                          32    4 × 10.sup.6 ≦                                                          59     1.5 × 10.sup.5                   300   51    1.1 × 10.sup.6                                                                 39    4 × 10.sup.6 ≦                                                          75     2.2 × 10.sup.4              2000  50   27    4 × 10.sup.6 ≦                                                          30    4 × 10.sup.6 ≦                                                          39        4 × 10.sup.6                                                         ≦                               100   39    4 × 10.sup.6 ≦                                                          49    2.1 × 10.sup.6                                                                 70     0.8 × 10.sup.5                   150   47    4 × 10.sup.6 ≦                                                          58    0.6 × 10.sup.6                                                                   80≦                                                                         0.03 × 10.sup.6             __________________________________________________________________________                                                4                             

As is apparent from Table 2, in the cases of the third and fourthexamples of the taper roller bearing according to the present invention,the temperature rise was suppressed, so that the bearings were scarcelyseized. That is, those bearings were lengthened in service life as much.

For instance in the case where the rotation speed is 1000 r.p.m., thefourth example is best in the outer race saturation temperature and thetotal number of revolutions which are obtained when the thrust load isincreased. This means that the fourth example is high in durability whenapplied to the case where the inner surface of the flange 11a is broughtinto slide contact with the end faces of the taper rollers 8 under highbearing pressure.

In the case where the rotation speed is 2000 r.p.m., the third exampleis best in the outer race saturation temperature and the total number ofrevolutions which are obtained when the thrust load is increased. Forinstance in the case where the thrust load is 150 kg, the outer racesaturation temperature in the third or fourth example is lower more than20° C. than that in the second comparative example, and the total numberof revolution is more than 100 times as large.

The relationships in magnitude between the outer race saturationtemperature and the total number of revolutions of the third example andthose of the fourth example are reversed depending on the changes inrotation speed. Hence, the third example is suitable as a roller bearingwhich is rotated at high speed, while the fourth example is suitable asa roller bearing which is rotated under high thrust load. At any rate,the third and fourth examples are superior in operation to the secondcomparative example under any using condition. As is apparent from theabove description, when operated under thrust load, the roller bearingof the present invention is proof against the generation of heatgeneration and the occurrence of seizure under the condition that theperipheral speed of the outer cylindrical surface, at the middle in theaxial direction, of the inner race (m/s=π×inner raceway diameter×numberof revolutions (/second)) is 1.6 m/s or larger.

In the above-described first through fourth examples, in order toenhance the binding of the surface layer 17 to the inner surface of therespective flange, the inner surface is treated by phosphating orsulphurizing; however, the present invention is not limited thereto orthereby. That is, for instance surface treatments using acid, andmechanical surface treatments such as barrelling, sand blasting and shotpeening may be employed.

Furthermore, in the above-described embodiments, the surface layer 17 isof the solid lubricant such as PTFE and molybdenum disulfide; however,the invention is not limited thereto or thereby. That is, for instancemineral materials and organic compounds effective in reducing thecoefficient of friction may be utilized for formation of the surfacelayer 17.

The roller bearing of the present invention is designed and functions asdescribed above. Therefore, even when its lubrication is insufficient,the temperature rise of the bearing is effectively suppressed. Hence,the roller bearing of the invention is scarcely seized; that is, it islengthened in service life. The roller bearing of the invention isapplicable to a variety of machines, improving the latter inreliability.

What is claimed is:
 1. A roller bearing comprising:an inner raceincluding an inner raceway on an outer cylindrical surface thereof; anouter race including an outer raceway on an inner cylindrical surfacethereof; a plurality of rollers rotatably provided between said innerraceway and said outer raceway; and a flange extending from an edge ofeither the outer cylindrical surface of said inner race or the innercylindrical surface of said outer race, said flange having an innersurface which is confronted with an end face of each of said rollers,wherein a surface layer is formed on confronting surfaces of the innersurface of said flange and the end face of each of said rollers, saidsurface layer comprising a solid lubricant, and an intermediate layer isformed between said surface layer and the confronting surfaces, theintermediate layer comprising a sulfide compound.
 2. The roller bearingof claim 1, wherein said solid lubricant is selected from the groupconsisting of molybdenum disulfide, polytetrafluoro-ethylene, and amixture of molybdenum disulfide and polytetrafluoro-ethylene.
 3. Theroller bearing of claim 2, wherein said rollers comprise cylindricalrollers.
 4. The roller bearing of claim 1, wherein said surface layer isformed from sid solid lubricant mixed in a macromolecular matrix whichis selected from the group consisting of epoxy, polyamideimide, and amixture of epoxy and polyamideimide.
 5. The roller bearing of claim 2,wherein said rollers comprise tapered rollers.
 6. The roller bearing ofclaim 4, wherein said rollers comprise cylindrical rollers.
 7. Theroller bearing of claim 4, wherein said rollers comprise taperedrollers.
 8. A roller bearing comprising:an inner race including an innerraceway on an outer cylindrical surface thereof; an outer race includingan outer raceway on an inner cylindrical surface thereof; a plurality ofrollers rotatably provided between said inner raceway and said outerraceway; and a flange extending from an edge of either the outercylindrical surface of said inner race or the inner cylindrical surfaceof said outer race, said flange having an inner surface which isconfronted with an end face of each of said rollers, wherein a surfacelayer is formed on confronting surfaces of the inner surface of saidflange and the end face of each of said rollers, said surface layercomprising a solid lubricant, and an intermediate layer is formedbetween said surface layer and the confronting surfaces by subjectingthe confronting surfaces to a surface treatment of sulphurizing.
 9. Theroller bearing of claim 8, wherein said solid lubricant is selected fromthe group consisting of molybdenum disulfide, polytetrafluoro-ethylene,and a mixture of molybdenum disulfide and polytetrafluoro-ethylene. 10.The roller bearing of claim 9, wherein said rollers comprise cylindricalrollers.
 11. The roller bearing of claim 9, wherein said rollerscomprise tapered rollers.
 12. The roller bearing of claim 8, whereinsaid surface layer is formed from said solid lubricant mixed in amacromolecular matrix which is selected from the group consisting ofepoxy, polyamideimide, and a mixture of epoxy and polyamideimide. 13.The roller bearing of claim 12, wherein said rollers comprise taperedrollers.
 14. The roller bearing of claim 12, wherein said rollerscomprise cylindrical rollers.